3b. Watersheds

Portland contains five watersheds, each with differing natural characteristics, hydrology, water quality, and habitat issues. In each of the watersheds, the future health of watersheds and the natural environment is dependent on addressing existing problems and on how future growth and development is managed. Portland’s watersheds:

Willamette River Watershed

Columbia Slough Watershed

Johnson Creek Watershed

Fanno Creek Watershed

Tryon Creek Watershed

Portland's watersheds are based around its rivers and largest urban streams. A watershed is an area that catches rain and snow, beginning at ridge tops and draining to a river, stream, lake, or wetland. Watershed health is influenced by the condition of natural hydrologic systems, water quality, physical habitat, and biological communities. The following highlights characteristics of Portland’s watersheds:

General characteristics of Portland’s watersheds

Roads, buildings and other impervious surfaces account for 22-36% of the surface coverage in Portland’s watersheds (from 22% in Tryon Creek to 36% in Columbia Slough).

Tree canopy covers approximately 26% of the City.

The City’s draft natural resource inventory identified over 200 miles of rivers and streams, and about 30,000 acres of riparian corridor and wildlife habitat.

Overall, water quality has improved, but each major water body has problems with bacteria, nutrients, and toxics.

The watersheds provide habitat for a plethora of fish, bird, mammal, amphibian and reptile species, including many with state and federal protected or “at risk” status.

Watershed councils and stewardship groups are instrumental in restoration efforts.

Willamette River Watershed

The river is 187 miles in length (the lower 17 miles, including the confluence with the Columbia River are in Portland); drainage area of 11,478 square miles (69 square miles in Portland).

Diverse topography of floodplain, low lands and steep drainages.

22% of area is parks/open space, including 5,000 acre Forest Park; 36% is inventoried natural resource area; 13% is protected by environmental zoning.